The present invention relates to bearings, more particularly to methodologies (such as involving lubrication) for reducing adverse effects (such as wear) associated with frictional contact characterizing bearing operation.
Bearings are used in a wide variety of machinery, including motors and other rotating machines. Bearings are frequently the first component of equipment to fail. Failure of rolling element bearings (e.g., ball bearings or roller bearings), for instance, is commonly associated with tribological effects (e.g., “wear and tear”) when insufficient lubrication is applied to the surfaces of the rolling elements (e.g., balls or rollers). Incorporated herein by reference are the following book excerpts, which are instructive concerning bearings and lubrication: Chapter 8.4 (pages 8-114 to 8-138; entitled “Fluid-Film Bearings”; by Dudley D. Fuller) of Marks' Standard Handbook for Mechanical Engineers, Ninth Edition, Eugene A. Avallone and Theodore Baumeister III, Editors, McGraw-Hill Book Company, New York, 1986, ISBN 0-07-004127-X; Chapter 8 (pages 352-392; entitled “Lubrication”) of Merhyle F. Spotts, Design of Machine Elements, Fifth Edition, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1978, ISBN 0-13-200576-X.
A longstanding objective in the bearing-related arts has been to improve the lubrication of bearings so as to minimize wear and extend the useful life of the bearings. Various methodologies have been proposed to achieve improved lubrication in bearings, such as disclosed by the following U.S. patents, each of which is incorporated herein by reference: Yabe et al. U.S. Pat. No. 6,228,813 B1 issued 8 May 2001; Brackett U.S. Pat. No. 6,193,014 B1 issued 27 Feb. 2001; Ryan et al. U.S. Pat. No. 6,180,574 B1 issued 30 Jan. 2001; Stephens et al. U.S. Pat. No. 6,280,090 B1 issued 28 Aug. 2001; Takasaki et al. U.S. Pat. No. 6,244,386 B1 issued 12 Jun. 2001; Hashimoto U.S. Pat. No. 6,290,397 B1 issued 18 Sep. 2001; and, Stephens et al. U.S. Pat. No. 6,280,090 B1 issued 28 Aug. 2001.
Yabe et al. disclose use of a polymer film to coat the race surfaces of a rolling element bearing. The bearing is filled with a polymer that contains lubricant; the lubricant is released as the rolling element exerts pressure on the film coating during operation. A disadvantage of this methodology is that, over time, the film releases all of its lubricant; the film itself becomes “lubricant starved.” Another disadvantage is that the properties of the film degrade over time due to polymer aging effects. The compression of the rolling element accelerates the aging effects, which consequently degrade the capabilities of the film to function as a lubricant-releasing agent.
Brackett discloses atomizing of pressurized air with a lubricant so as to provide a spray mist. A disadvantage of this methodology is that, once the mist has been deposited onto the race, it is then free to flow from and/or drip off the race; that is, the lubricant is not “secured” to the surface of the race, but can leave the race due to the action of gravity. Furthermore, generally speaking, the viscosity of a lubricant is temperature-dependent, the viscosity decreasing with increasing temperature. The viscosity of the lubricant determines its flow and drip characteristics; that is, when the viscosity of the lubricant decreases, the lubricant flows faster. Thus, when operating temperature conditions change, so too will the flow and drip characteristics of the lubricant. Therefore, according to the methodology of Brackett, under some operating conditions the lubricant will flow or drip from the race surface faster than under other operating conditions; at higher temperatures, the viscosity of the lubricant will be lower and the flow rate of the lubricant (e.g., away from the race) will be higher. Under operating conditions of lower viscosity and higher flow, if too much lubricant flows away then insufficient residual lubricant remains on the race, the bearing thus remaining “lubricant-starved.”
Ryan et al. disclose application of a solid lubricant coating to a bearing. A disadvantage is that the solid lubricant of Ryan et al. functions as a result of wearing away; that is, small particles of solid lubricant are shaved off of the coating by the rolling element as the rolling element moves along race surface. The coating is eventually worn away because the number of particles shaved off increases over time. Moreover, as Ryan et al.'s coating is worn away, the increasing clearance between the rolling elements and the races leads to problems relating to vibration.
The bearings disclosed by Takasaki et al. and Hashimoto involve the flinging or flowing of lubricating fluid onto a bearing surface by means of a component that picks up the lubricating fluid as the shaft and inner race turn. The bearing lubrication approaches of Takasaki et al. and Hashimoto are disadvantageous similarly as is that of Brackett. The lubricant is free to flow or drip from the race surface(s) once it is flung or flowed onto the race surface(s). Further, the flow rate away from the race surface is dependent upon the viscosity of the lubricant and is therefore temperature-dependent.
Stephens et al. disclose “microstructures” (e.g, “microchannels” or “microposts”) to help distribute lubricant in a bearing. A disadvantage of Stephens' microstructures is that, since the surfaces they form are uneven (unsmooth), the distribution of compression forces acting on a bearing element, and hence the wear of the bearing element, is uneven. The surface areas formed by the “peaks” (highest elevations) of the microstructures are subjected to higher compression forces, and hence are prone to greater wear, than are the less elevated surface areas.